Due to the quick development in the electronic and semiconductor industrial fields, the progress in the process technology and the trends in market demands, various electronic devices have been designed to have compact volume and low weight. While the currently available electronic devices are gradually reduced in size, they actually have constantly increased functions and computing ability. For example, among other information electronic products, the most popular notebook computers and desktop computers all include many electronic components that generate heat during actual operation thereof. Particularly, the central processing unit (CPU) would generate the largest part of heat in the computer. Currently, a heat sink composed of radiating fins and a cooling fan is often used to provide heat dissipation function and plays an important role in protecting the CPU against accumulated heat, so that the CPU can be maintained at a normal working temperature to provide its intended functions. In brief, the CPU heat sink has become a highly important component in the present information electronic industry.
In recent years, water-cooling technique has been widely applied to personal computers for heat dissipation. With the water-cooling technique, the radiating fins occupying a large space are omitted, and heat generated by the heat source in an electronic system is collected by a working liquid; and then, a heat exchanger exchanges the collected heat with ambient air. Since the pipeline included in a water-cooling system for delivering the working liquid is length changeable according to actual need, the heat exchanger can be flexibly located at different places. That is, the heat exchanger, i.e. a radiating fin assembly, can be freely designed without being restricted by the space available for mounting it. However, the water-cooling system requires a pump for driving the working liquid to flow through the pipeline, and a water reservoir for storing the working liquid. Therefore, the water-cooling system is subject to some risks, such as the reliability of the pump and leakage of the pipeline.
Therefore, heat pipe is still the currently most frequently used technique in heat transfer, and radiating fins are still needed to exchange the heat transferred via the heat pipe with the ambient air. In some cases, the heat pipe and other heat dissipation elements are internally provided with a micro structure to enable increased heat dissipation efficiency. Meanwhile, other means are also tried to minimize the power consumption of the CPU in order to reduce the heat generated by the CPU.
FIG. 1 is a sectional view of a conventional loop-type thermal module 8. As shown, the thermal module 8 includes a heat-absorption element 81 having an outlet 811 and an inlet 812, and being filled with a working fluid 84; a condensing element 82 including a plurality of radiating fins 821; and a pipeline 83 connecting the condensing element 82 to the heat-absorption element 81 to form a heat-transfer loop.
The pipeline 83 includes a first section 831, a second section 832, and a third section 833. The first section 831 is extended between the outlet 811 of the heat-absorption element 81 and the condensing element 82; the second section 832 is bent to extend through the condensing element 82 several times; and the third section 833 is extended between the condensing element 832 and the inlet 812 of the heat-absorption element 81. It is noted the pipeline 83 including the first, second and third sections 831, 832, 833 is an integrally formed pipeline.
The heat-absorption element 81 is in contact with at least one heat-generating element 9 for absorbing heat generated by the element 9. The working fluid 84 in the heat-absorption element 81 is heated by the absorbed heat to change from liquid phase into vapor phase. The vapor-phase working fluid 84 flows out of the heat-absorption element 81 via the outlet 811 and flows through the first section 831 of the pipeline 83 to carry and transfer the absorbed heat to the condensing element 82. When the vapor-phase working fluid 84 flows through the second section 832 of the pipeline 83 that winds through the condensing element 82, the heat carried by the vapor-phase working fluid 84 is absorbed by the condensing element 82. The heat absorbed by the condensing element 82 is then radiated into the ambient air and dissipated, and the vapor-phase working fluid 84 flowed through the second section 832 is cooled and condensed into liquid phase again. The liquid-phase working fluid 84 keeps flowing through the second and the third section 832, 833 of the pipeline 83 back to the heat-absorption element 81 for the next cycle of vapor-liquid circulation.
After changing from vapor phase into liquid phase in the second section 832 of the pipeline 83, the working fluid 84 slowly flows back to the heat-absorption element 81 simply under the action of the gravity force. Thus, areas at middle, rear and bent portions of the second section 832 form ineffective areas that are little helpful in increasing the flow-back efficiency of the working fluid 84.
Therefore, the conventional thermal module 8 has the following disadvantages: (1) providing only low heat transfer effect; (2) forming areas of ineffective heat transfer; and (3) requiring high manufacturing cost.